The present invention relates to a printer driving apparatus which is used for a line printer.
Hitherto, as a line printer of the dot matrix type, a construction such that each character is divided into dots and a print head is driven by a plurality of print cycles to thereby print has been known. The above conventional printer driving apparatus will now be described hereinbelow with reference to the drawings.
FIG. 1 is a circuit diagram showing a prior printer driving apparatus. FIG. 2 is an explanatory diagram showing print timings in the above prior art. FIG. 3 is an explanatory diagram showing a print example. FIG. 4 is an explanatory diagram showing an example of data stored in a print buffer in the prior art.
In FIG. 1, reference numeral 51 denotes a print head; 52 a print buffer to store print data; 53 a driving circuit to drive dots of the print head 51 in correspondence to the data in the print buffer 52 and strobe signals I, II, III, and IV; 54 a paper feed motor; 55 a driving circuit to drive the paper feed motor 54; and 56 a power source.
The operation in the above construction will now be described hereinbelow.
It is now assumed that numbers "1234" of four digits shown in the print example of FIG. 3 are printed. Each of the numbers 4, 3, 2, and 1 of each digits is divided into 72 (=8.times.9) dots and is printed by driving the print head 51 of 32 dots by the driving circuit 53 by total nine print cycles of the first to ninth print cycles. As shown in FIG. 4, the data to be printed every print cycle have been stored in the print buffer 52. A power source of a large capacity is needed to drive the 32 dots of the print head 51 in a lump in correspondence to total 32 dots of each print cycle of the characters of four digits. Therefore, as shown in FIGS. 1 and 2, by making the driving circuit 53 operative on the basis of the data in the print buffer 52 in correspondence to the strobe signals I to IV, a current is supplied to the print head 51. In the first print cycle, the 32 dots are divided into four groups of the 1st to 8th dots, the 9th to 16th dots, the 17th to 24th dots, and the 25th to 32nd dots for each of the numbers 4, 3, 2, and 1 of each digit. Those dots are driven every group and printed.
To print the next dots after completion of the printing, the motor 54 is driven by the driving circuit 55, thereby feeding a print paper. In a manner similar to the above, in each of the second to ninth print cycles, the 32 dots of the print head 51 are divided into four groups every number of each digit and printed.
As mentioned above, in the printer driving apparatus of the conventional example, the power source load is reduced into by a factor of 4, and the printing is executed in a predetermined printing time.
However, in the driving timings of the conventional example, a division ratio of the dots of the print head 51 in each print cycle is always constant. Therefore, the power source capacity such that all dots can be printed in one print cycle is needed and the power source is expensive. There is also a problem such that the printing time is constant or the like.